The present invention relates to a storage container filled with carbon dioxide containing a functional material (modifying material), and a method for molding a resin and a method for forming a plating film, by using carbon dioxide containing the functional material.
The electroless plating method has been hitherto widely used as a method for forming a metal conductive film on a surface of an electronic device comprised of a plastic structural member. The electroless plating process for the plastic somewhat varies depending on, for example, the material of the plastic. However, in general, the respective steps of resin molding, degreasing of a molded article, etching, neutralization and wetting, addition of catalysts, activation of catalysts, and electroless plating are performed in this order.
For example, a chromic acid solution or an alkali metal hydroxide solution is used as the etching solution in the etching step of the electroless plating process described above, and results in the factor to increase the cost, because the etching solution as described above requires any aftertreatment such as the neutralization. Further, a highly toxic etchant is used in the etching step of the electroless plating process described above. Therefore, a problem arises in relation to the handling in view of the environment. In Europe, the instruction of RoHS (Restriction of the use of certain Hazardous Substances in electrical and electric equipment) has been established, which restricts specified harmful chemical substances contained in electric and electronic products. Materials and parts supply manufacturers are required to guarantee the fact that hexavalent chromium or the like is not contained in new electric and electronic devices to be introduced into the European market after Jul. 1, 2006. In view of the circumstances as described above, the conventional electroless plating process for the plastic, which involves the large environmental load, is confronted with the essential task to make the transfer to any substitutive technique.
In order to dissolve the problem involved in the conventional technique for forming the electroless plating film for the plastic, for example, a novel plastic electroless plating method, which is based on the use of the supercritical fluid, is proposed in “Latest Application Technique for Supercritical Fluid” (written by Teruo HORI, NTS Publication, pp. 250-255 (2004)). According to the method described in “Latest Application Technique for Supercritical Fluid”, the metal complex can be injected into the polymer surface by dissolving the organic metal complex in carbon dioxide in the supercritical state (hereinafter referred to as “supercritical carbon dioxide” as well) to bring into contact with various types of polymers. Metallic fine particles are deposited on the polymer surface by performing the reducing treatment such as the chemical reducing treatment or the heating for the polymer into which the metal complex is injected. Accordingly, the entire polymer surface can be subjected to the electroless plating. According to this process, it is seen that the electroless plating process for the plastic having the good surface roughness can be achieved, in which it is unnecessary to perform any treatment for the waste liquid.
The present inventors have suggested, for example, in Japanese Patent No. 3696878, a method for producing a molded article in which a functional material such as a metal complex is dissolved beforehand in supercritical carbon dioxide, and the functional material is impregnated into the surface of the molded article during the injection molding by applying the principle described in “Latest Application Technique for Supercritical Fluid”. In this method, the functional material is impregnated into the melted resin by bringing the supercritical carbon dioxide, in which the functional material has been dissolved, into contact with the melted resin. After that, the injection molding is performed to produce the molded article.
A foam molding process is suggested as an injection molding process industrially practiced by utilizing the supercritical fluid, for example, in Japanese Patent Application Laid-open No. 2001-150504. In the molding method disclosed in Japanese Patent Application Laid-open No. 2001-150504, an inert gas such as N2 or carbon dioxide is used as a foaming agent without using any conventional chemical foaming agent. The inert gas in the supercritical state is kneaded with a melted resin. The kneading is performed while mixing a resin material to be plasticized and melted and a supercritical fluid such as N2 or CO2 in a screw when the resin material is plasticized and weighed by using the screw.
Various methods have been also hitherto suggested as techniques for modifying the polymer by utilizing the supercritical fluid in order to provide the highly advanced function such as, for example, the improvement in the wettability of the surface of the polymer base material. For example, Japanese Patent Application Laid-open No. 2001-226874 discloses the method for forming the hydrophilic fiber surface by bringing dissolving a supercritical fluid, in which polyalkyl glycol has been dissolved, into contact with the fiber. Japanese Patent Application Laid-open No. 2002-129464 discloses a batch process to realize the highly advanced function of a surface of a polymer base material. Specifically, the supercritical fluid, in which the solute as the functional material has been previously dissolved, is brought into contact with the polymer base material in a supercritical state, i.e., at a high pressure to perform the dyeing.
Japanese Patent Application Laid-open No. 2002-313750 also discloses the following method. At first, a mask, in which holes having desired shapes are formed, is provided on a substrate. Then, a supercritical fluid, in which a substance (metal complex) to be adhered onto the substrate has been dissolved, is jetted onto the mask to form a pattern of not more than 100 μm of the adhered substance on the substrate.
Further, for example, a method is also suggested in Japanese Patent Application Laid-open No. 2005-305945, in which a plating catalyst core (metal complex) is impregnated into a part of surface of a polymer base material by using a technique for modifying the surface of the polymer base material based on the use of a supercritical fluid, and then, a plating film is formed on the polymer base material. In Japanese Patent Application Laid-open No. 2005-305945, the following method is suggested as a method for selectively impregnating the metal complex into the part of the surface of the polymer base material. At first, the metal complex is added to a wide area or the entire area of the surface of the polymer base material. Subsequently, a mold surface, which has a predetermined concave/convex pattern, is brought into tight contact with or adhesion to the surface of the polymer base material. Subsequently, the supercritical fluid is allowed to flow into the space defined by the mold (concave portion or recess) and the surface of the polymer base material. The metal complex is selectively impregnated into only the surface area of the polymer base material into which the supercritical fluid is allowed to flow.
The method, which is disclosed in “Latest Application Technique for Supercritical Fluid” described above, is the batch process. Therefore, this method can be industrially practiced when a large amount of fiber, sheet or the like can be processed in a high pressure vessel. However, in this principle, the polymer surface is softened by the supercritical carbon dioxide or the like, and the supercritical fluid and the metal complex as the modifying material (functional material) are impregnated into the polymer. Therefore, when a large-sized injection molding article or plastic is produced, the method is difficult to be industrially practiced, because it is difficult to maintain the shape of the polymer by softening thereof. Further, the high pressure vessel and the apparatus for generating the supercritical carbon dioxide are the factors to increase the cost.
Nitrogen or carbon dioxide in the supercritical state is also brought into contact with the resin in the melted state or the solidified state in the techniques disclosed in Japanese Patent No. 3696878 and Japanese Patent Application Laid-open Nos. 2001-150504, 2001-226874, 2002-129464, 2002-313750, and 2005-345945 described above. The apparatus for generating the supercritical fluid is the factor to increase the cost in the same manner as in the technique disclosed in “Latest Application Technique for Supercritical Fluid” described above.
More specifically, in the case of the conventional technique as described above, when carbon dioxide is used as the medium for dissolving the functional material, it is necessary that the pressure is previously raised to not less than 7.38 MPa, and the temperature is raised to not less than 31° C. to provide the supercritical state. Therefore, the task resides in the long term reliability of the seal of the piping and the apparatus for generating the supercritical fluid. Further, it is necessary to provide a step of pressurizing carbon dioxide and an expensive high pressure pump and/or a high pressure dissolution tank for dissolving the solute (functional material). These matters bring about the factor to increase the cost when the molded article is mass-produced.